Organic light-emitting diodes and methods for assembly and emission control

ABSTRACT

New organic light-emitting diodes and related electroluminescent devices and methods for fabrication, using siloxane self-assembly techniques.

[0001] This invention was conceived under grant from the Office of NavalResearch through the Center for Advanced Multi-Functional NonlinearOptical, Polymers and Molecular Assemblies (“CAMP”), grant no. MURIN00014-95-1-1319, and from the National Science Foundation, grant no.DMR-9632472. The U.S. Government retains certain rights in thisinvention pursuant to such finding.

BACKGROUND OF THE INVENTION

[0002] This invention relates generally to organic electroluminescentdevices with organic films between anodic and cathodic electrodes, andmore particularly to such devices and methods for their assembly usingthe condensation of various silicon moieties.

[0003] Organic electroluminescent devices have been known, in variousdegrees of sophistication, since the early 1970's. Throughout theirdevelopment and consistent with, their function and mode of operation,they can be described generally by way of their physical construction.Such devices are characterized generally by two electrodes which areseparated by a series of layered organic films that emit light when anelectric potential is applied across the two electrodes. A typicaldevice can consist, in sequence, of an anode, an organic hole injectionlayer, an organic hole transport layer, an organic electron transportlayer, and a cathode. Holes are generated at a transparent electrode,such as one constructed of indium-tin-oxide, and transported through ahole-injecting or hole-transporting layer to an interface with anelectron-transporting or electron-injecting layer which transportselectrons from a metal electrode. An emissive layer can also beincorporated at the interface between the hole-transporting layer andthe electron-transporting layer to improve emission efficiency and tomodify the color of the emitted light.

[0004] Significant progress has been made in the design and constructionof polymer and molecule-based electroluminescent devices, forlight-emitting diodes, displays and the like. Other structures have beenexplored and include the designated “DH” structure which does notinclude the hole injection layer, the “SH-A” structure which does notinclude the hole injection layer or the electron transport layer, andthe “SH-B” structure which does not include the hole injection layer orthe hole transport layer. See, U.S. Pat. No. 5,457,357 and in particularcol. 1 thereof, which is incorporated herein by reference in itsentirety.

[0005] The search for an efficient, effective electroluminescent deviceand/or method for its production has been an ongoing concern. Severalapproaches have been used with certain success. However, the prior arthas associated with it a number of significant problems anddeficiencies. Most are related to the devices and the methods by whichthey are constructed, and result from the polymeric and/or molecularcomponents and assembly techniques used therewith.

[0006] The fabrication of polymer-based electroluminescent devicesemploys spin coating techniques to apply the layers used for the device.This approach is limited by the inherently poor control of the layerthickness in polymer spin coating, diffusion between the layers,pinholes in the layers, and inability to produce thin layers which leadsto poor light collection efficiency and the necessity of high D.C.driving voltages. The types of useful polymers, typicallypoly(phenylenevinylenes), are greatly limited and most areenvironmentally unstable over prolonged use periods.

[0007] The molecule-based approach uses vapor deposition techniques toput down thin films of volatile molecules. It offers the potential of awide choice of possible building blocks, for tailoring emissive andother characteristics, and reasonably precise layer thickness control.Impressive advances have recently been achieved in molecular buildingblocks—especially in electron transporters and emitters, layer structuredesign (three versus two layers), and light collection/transmissionstructures (microcavities).

[0008] Nevertheless, further advances must be made before these devicesare optimum. Component layers which are thinner than achievable byorganic vapor deposition techniques would allow lower DC drivingvoltages and better light transmission collection characteristics. Manyof the desirable, component molecules are nonvolatile or poorlyvolatile, with the latter requiring expensive high vacuum or MBE growthequipment. Such line-of-site growth techniques also have limitation interms of conformal coverage. Furthermore, many of the desirablemolecular components do not form smooth, pinhole-free, transparent filmsunder these conditions nor do they form epitaxial/quasiepitaxialmultilayers having abrupt interfaces. Finally, the mechanical-stabilityof molecule-based films can be problematic, especially for large-areaapplications or on flexible backings.

[0009] In order to realize high resolution information displays, themicrofabrication of light-emitting diodes and pixel arrays is required.So far, several approaches have been employed. One such approachinvolves patterning the anode and/or cathode of the device structure,the other patterning the emitting materials. The bottom ITO electrode iscommonly patterned using a combination of standard photolithography andwet chemical etching, while the top electrode is typically defined bydeposition through a shadow mask. Generally, there are disadvantagesassociated with each of these procedures, such as the difficulty ofprecise shadow mask alignment for multiple deposition, and frequent maskreplacement or cleaning for high dimensional control of the underlyingdisplay panel. Alternatively, the cathode and/or anode could be alteredusing laser ablation. However, with patterned substrates, vacuumdeposition of the organic materials not efficiently coat the steep edgesand sharp corners of the anode, thereby resulting in poor coverage whichcan lead to cathode-to-anode short circuits.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010]FIGS. 1A and 1B show structural formulae for porphyrinic compoundswhich are illustrative examples of compounds of the type which can beused as hole injection components/agents in the preparation of themolecular conductive or hole injection layers and electroluminescentmedia of this invention. In FIG. 1, M is Cu, Zn, SiCl₂, or 2H; Q is N orC(X), where X is a substituted or unsubstituted alkyl or aryl group, andR is H, trichlorosilyl, trialkoxysilyl, or a moiety having 1 to 6 carbonatoms which can include trichlorosilyl or trialkoxysilyl groups,substituted on the C₁-C₄, C₈-C₁₁ C₁₅-C₁₈ and/or C₂₂-C₂₅ positions. InFIG. B, M is Cu, Zn, SiCl₂, or 2H; Q is N or C(X), where X is asubstituted or unsubstituted alkyl, or aryl group; and T₁/T₂ is H,trichlorosilyl, trialkoxysilyl, or a moiety having 1 ton 6 carbon atomswhich can include trichlorosilyl or trialkoxysilyl groups.

[0011] FIGS. 2A-2C show structural formulae for arylamine compoundswhich are illustrative examples of compounds of the type which can beused as hole transport compounds/agents in the preparation of themolecular conductive or hole transport layers and electroluminescentmedia of this invention. In FIG. 2A, R₂, R₃ and/or R₄ can be H,trihalosilyl, trialkoxysilyl, dihalosilyl, dialkoxysilyl, or a moietyhaving 1 to 6 carbon atoms which can include dialkyldichlorosilyl,dialkyldialkoxysilyl, trichlorosilyl or trialkoxysilyl groupssubstituted anywhere on the aryl positions. In FIG. 2B, Q₁ and Q₂ can besubstituted or unsubstituted tertiary aryl amines, such as thosedescribed with FIG. 2A; and G is a linking group to include but notlimited to an alkyl, aryl, cylcohexyl or heteroatom group. In FIG. 2C,Ar is an arylene group; n is the number of arylene groups from 1-4; andR₅, R₆, R₇, and/or R₈ can be H, trihalosilyl, trialkoxysilyl,dihalosilyl, dialkoxysilyl or a moiety having 1 to 6 carbon atoms whichcan include dialkyldichlorosilyl, dialkyldialkoxysilyl, trichlorosilylor trialkoxysilyl groups substituted anywhere on the aryl positions.

[0012] FIGS. 3A-3C show structural formulae for aryl compounds which areillustrative of examples of compounds of the type which can be used asemissive compounds/agents in the preparation of the molecular conductivelayers and electroluminescent media of this invention. In FIG. 3A, R₉and R₁₀ can be H, trihalosilyl, trialkoxyslyl, dihalosilyl, alkoxysilyl,or a moiety having 1 to 6 carbon atoms which can includedialkyldichlorosilyl, dialkyldialkoxysilyl, trichlorosilyl ortrialkoxysilyl groups substituted anywhere on the aryl positions. InFIG. 3B, M is Al or Ga; and R₁₁-R₁₄ can be H, trihalosilyl,trialkoxysilyl, dihalosilyl, dialkoxysilyl, or a moiety having 1 to 6carbon atoms which can include dialkyldichlorosilyl,dialkyldialkoxysilyl, trichlorosilyl or trialkoxysilyl groupssubstituted anywhere on the aryl positions. In FIG. 3C Ar is arylene;and R₁₅-R₁₈ can be H, trihalosilyl, trialkoxysilyl, dihalosilyl,dialkoxysilyl, or a moiety having 1 to 6 carbon atoms which can includedialkyldichlorosilyl, dialkyldialkoxysilyl, trichlorosilyl ortrialkoxysilyl groups substituted anywhere on the aryl positions.

[0013] FIGS. 4A-4C show structural formulae for heterocyclic compoundswhich are illustrative examples of compounds of the type which can beused as electron transport components/agents in the preparation, of themolecular conductive or electron transport layers and inelectroluminescent media of this invention. In FIGS. 4A-4C, X is O or S;and R₁₉-R₂₄ can be aryl groups substituted with the followingsubstituents anywhere on the aryl ring: trihalosilyl, trialkoxysilyl,dihalosilyl, dialkoxysilyl, or a moiety having 1 to 6 carbon atoms whichcan contain dialkyldichlorosilyl, dialkyldialkoxysilyl, trichlorosilylor trialkoxysilyl groups.

[0014]FIGS. 5A and 5B (ITO is indium-tin-oxide, HTL is hole transportlayer and ETL is electron transport layer) show, schematically and in astep-wise manner by way of illustrating the present invention, use ofthe components/agents of Examples 1-5 and FIGS. 1-4 in the self-assemblyand preparation of an organic light-emitting diode device. Inparticular, the molecular representation FIG. 5A illustrates thehydrolysis of an assembled silicon/silane component/agent to provide anSi—OH functionality reactive toward a silicon/silane moiety of anothercomponent, agent or conductive layer. The block and molecularrepresentations of FIG. 5B illustrate a completed assembly.

[0015]FIG. 6 shows an alternative synthetic sequence enroute to severalarylamine components/agents, also in accordance with the presentinvention.

[0016]FIG. 7 shows, schematically and by way of illustrating analternative embodiment of the present invention, use of thecomponents/agents of FIG. 6 in the preparation of another representativeelectroluminescent device.

[0017]FIG. 8 graphically correlates x-ray reflectivity measurements offilm thickness with the number of capping layers applied to a substrate.As calculated from the slope of the line (y=8.3184x), each layer isabout 7.84 Å in dimensional thickness.

[0018]FIG. 9 graphically shows cyclic voltametry measurements, using10⁻³M ferrocene in acetonitrile, taken after successive layer (c-e)deposition and as compared to a bare ITO electrode (a). Even one cappinglayer (b), in accordance with this invention, effectively blocks theelectrode surface. Complete blocking is observed after deposition ofthree or four layers. The sweep rate was 100 mV/sec, and the electrodearea was about 0.7 cm².

[0019] FIGS. 10A-C graphically illustrate various utilities and/orperformance, characteristics (current density, quantum efficiency andforward light output, respectively, versus voltage) achievable throughuse of the present invention, as a function of the number of cappinglayers on an electrode surface: 0 layers, bare ITO (⋄), 1 layer, 8 Å(□), 2 layers, 17 Å (), 3 layers, 25 Å (▴) and 4 layers, 33 Å (∇).Reference is made to example 10.

[0020]FIG. 11 is a schematic diagram showing, generally a contactprinting procedure of the type which can be used in conjunction tofabricate the present invention.

[0021] FIGS. 12A-12C illustrates schematically various structures of anelectroluminescent article, in accordance with the present invention, ascan be prepared and patterned using a method described herein and/or asillustrated in FIG. 11. Articles such as those shown in FIGS. 12A-12Cand constructed as described herein can provide a patterned pixel array.As shown, in FIG. 12A, the shaded areas of FIGS. 12B and 12C represent apatterned control layer.

[0022]FIG. 13 is a photograph of the pixel array attainable through useof an organic light-emitting device, in accordance with this invention.The photograph was taken under ambient light conditions and correlatesto a device structures such as those illustrated in FIGS. 12A-12C.

[0023] FIGS. 14-16 show current-voltage data (FIG. 14) and lightoutput-voltage data (FIG. 15) for an article of this invention having apixel array which can be fabricated using the methodologies describedherein. The insets of each expand the 15V-18V region. FIG. 16 shows(dotted line) where an increase in voltage provides for emission throughthe entire luminescent area, not just through the pixel display.

SUMMARY OF THE INVENTION

[0024] In light of the foregoing, it is an object of the presentinvention to provide electroluminescent articles and/or devices andmethod(s) for their production and/or assembly, thereby overcomingvarious deficiencies and shortcomings of the prior art, including thoseoutlined above. It will be understood by those skilled in the art thatone or more aspects of this invention can meet certain objectives, whileone or more other aspects can meet certain other objectives. Eachobjective may not apply equally, in all its respects, to every aspect ofthis invention. As such, the following objects can be viewed thealternative with respect to anyone aspect of this invention.

[0025] It is an object of the present invention to provide control overthe thickness dimension of a luminescent medium and/or the conductivelayers of such a medium, to control the wavelength of light emitted fromany electroluminescent device and enhance the efficiency of suchemission.

[0026] It can be another object of the present invention to providemolecular components for the construction and/or modification of anelectroluminescent medium and/or the conductive layers thereof, whichwill allow lower driving and/or turn-on voltages than are availablethrough use of conventional materials.

[0027] It can also be an object of the present invention to providecomponent molecules which can be used effectively in liquid mediawithout resort to high vacuum or MBE growth equipment.

[0028] It can also be an object of the present invention to provideconformal conductive layers and the molecular components thereof whichallows for the smooth, uniform deposition on an electrode, substratesurface and/or previously-deposited layers.

[0029] It can also be an object of this invention to provide anelectroluminescent medium having a hybrid structure and where one ormore of the layers is applied by a spin-coat or vapor depositiontechnique to one or more self-assembled conductive layers.

[0030] Other objects, features and advantages of the present inventionwill be apparent from this summary of the invention and its descriptionsof various preferred embodiments, and will be readily apparent to thoseskilled in the art having knowledge of various electroluminescentdevices and assembly/production techniques. Such subjects, features,benefits and advantages will be apparent from the above, as taken intoconjunction with the accompanying examples, data, figures and allreasonable inferences to be drawn therefrom, alone or with considerationof the references incorporated herein.

[0031] This invention describes, in part, a new route to the fabricationof light emitting organic multilayer heterojunction devices, useful forboth large and small, multicolored display applications. As, describedmore fully below, electron and hole transporting layers, as well as theemissive layer, as well as any other additional layers, are applied,developed and/or modified by molecular self-assembly techniques. Assuch, the invention can provide precise control over the thickness of aluminescent medium or the conductive layers which make up such a medium,as well as provide maximum light generation efficiency. Use of thepresent invention provides strong covalent bonds between the constituentmolecular components, such that the mechanical, thermal, chemical and/orphotochemical stability of such media and/or conductive layers, as canbe used with an electroluminescent device, are enhanced. The use of suchcomponents also promotes conformal surface coverage to prevent cracksand pinhole deformities.

[0032] More specifically, the siloxane self-assembly techniquesdescribed herein allow for the construction of molecule-basedelectroluminescent media and devices. As described more fully below,various molecular components can be utilized to control the thicknessdimension of the luminescent media and/or conductive layers. Nanometerdimensions can be obtained, with self-sealing, conformal coverage. Theresulting covalent, hydrophobic siloxane network imparts considerablemechanical strength, as well as enhancing the resistance of such mediaand/or devices to dielectric breakdown, moisture intrusion, and otherdegradative processes.

[0033] In part, the present invention is an electroluminescent articleor device which includes (1) an anode, (2) a plurality of molecularconductive layers where one of the layers is coupled to the anode withsilicon-oxygen bonds and each of the layers is coupled one to anotherwith silicon-oxygen bonds, and (3) a cathode in the electrical contactwith the conductive layers. More generally and within the scope of thisinvention, an anode is separated from a cathode by an organicluminescent medium. The anode and the cathode are connected to anexternal power source by conductors. The power source can be acontinuous direct, alternating or an intermittent current voltagesource. A convenient conventional power source, including any desiredswitching circuitry, which is capable of positively biasing the anodewith respect to the cathode, can be employed. Either the anode, orcathode can be at ground potential.

[0034] The conductive layers can include but are limited to a holetransport layer, a hole injection layer, an electron transport layer andan emissive layer. Under forward biasing conditions, the anode is at ahigher potential than the cathode, and the anode injects holes (positivecharge carriers) into the conductive layers and/or luminescent mediumwhile the cathode-injects electrons therein. The portion of thelayers/medium adjacent to the anode forms a hole injecting and/ortransporting zone while the portion of the layers/medium adjacent to thecathode forms an electron injecting and/or transporting zone. Theinjected holes and electrons each migrate toward the oppositely chargedelectrode, resulting in hole-electron interaction within the organicluminescent medium of conductive layers. A, migrating electron dropsfrom its conduction potential to a valence band in filling a hole torelease energy as light. In such a manner, the organic luminescentlayers/medium between the electrodes performs as a luminescent zonereceiving mobile charge carriers from each electrode. Depending upon theconstruction of the article/device, the released light can be emittedfrom the luminescent conductive layers/medium through one or more ofedges separating the electrodes, through the anode, through the cathodeor through any combination thereof. See U.S. Pat. No. 5,409,783 and, inparticular cols. 4-6 and FIG. 1 thereof, which is incorporated herein byreference in its entirety. As would be understood by those skilled inthe art, reverse biasing of the electrodes will reverse the direction ofmobile charge migration, interrupt charge injection, and terminate lightemission. Consistent with the prior art, the present inventioncontemplates a forward biasing DC power source and reliance on externalcurrent interruption or modulation to regulate light emission.

[0035] As demonstrated and explained below, it is possible to maintain acurrent density compatible with efficient light emission while employinga relatively low voltage across the electrodes by limiting the totalthickness of the organic luminescent medium to nanometer dimensions. Atthe molecular dimensions possible through use of this invention, anapplied voltage of less than about 10 volts is sufficient for efficientlight emission. As discussed more thoroughly herein, the thickness ofthe organic luminescent conductive layers/medium can be designed tocontrol and/or determine the wavelength of emitted light, as well asreduce the applied voltage and/or increase in the field potential.

[0036] Given the nanometer dimensions of the organic luminescentlayers/medium, light is usually emitted through one of the twoelectrodes. The electrode can be formed as a translucent or transparentcoating, either on the organic layer/medium or on a separate translucentor transparent support. The layer/medium thickness is constructed tobalance light transmission (or extinction) and electrical conductance(or resistances other considerations relating to the design,construction and/or structure of such articles or devices are asprovided in the above referenced U.S. Pat. No. 5,409,783, suchconsiderations as would be modified in accordance with the molecularconductive layers and, assembly methods of the present invention.

[0037] In preferred embodiments, the conductive layers have molecularcomponents, and each molecular component has at least two siliconmoieties. In highly preferred embodiments, each silicon moiety is ahalogenated or alkoxylated silane and silicon-oxygen bonds are obtainable from the condensation of the silane moieties with hydroxy,functionalities. In preferred embodiments, the present invention employsan anode with a substrate having a hydroxylated surface portion. Thesurface portion is transparent to near IR and visible wavelengths oflight. In such highly preferred embodiments the hydroxylated surfaceportions include SiO₂, In₂·SnO₂, Ge and Si, among other such materials.

[0038] In conjunction with anodes and the hydroxylated surface portionsthereof, the conductive layers include molecular components, and eachmolecular component has at least two silicon moieties. As discussedabove, in such embodiments, each silicon moiety is a halogenated oralkoxylated silane, and silicon-oxygen bonds are obtainable from thecondensation of the silane moieties with hydroxy functionalities whichcan be on a surface portion of an anode. Consistent with such preferredembodiments, a cathode is in electrical contact with the conductivelayers. In highly preferred embodiments, the cathode is vapor, depositedon the conductive layers, and constructed of a material including Al,Mg, Ag, Au, In, Ca and alloys thereof.

[0039] In part, the present invention is a method of producing alight-emitting diode having enhanced stability and light generationefficiency. The method includes (1) providing an anode with ahydroxylated surface; (2) coupling the surface to a hole transport layerhaving a plurality of molecular components, with each component havingat least two silicon moieties reactive with the surface, with couplingof one of the silicon moieties to form silicon-oxygen bonds between thesurface and the hole transport layer; (3) coupling the hole transportlayer to an electron transport layer, the electron transport layerhaving a plurality of molecular components with each of the componentshaving at least two silicon moieties reactive with the hole transportlayer, with the coupling of one of the silicon moieties to formsilicon-oxygen bonds between the hole and electron transport layers; and(4) contacting the electron transport layer with a cathode material.

[0040] In preferred embodiments of this method, the hole transport layerincludes a hole injecting zone of molecular components and a holetransporting zone of molecular components. Likewise, in preferredembodiments, each silicon moiety is a halogenated or alkoxylated silanesuch that, with respect to this embodiment, coupling the hole transportlayer to the electron transport layer further includes hydrolyzing thehalogenated or alkoxylated silane. Likewise, with respect to ahalogenated or alkoxylated silane embodiment, contacting the electrontransport layer with the cathode further includes hydrolyzing thesilane.

[0041] In part, the present invention is a method of controlling thewavelength of light emitted from an electroluminescent device. Theinventive method includes (1) providing in sequence a hole transportlayer, an emissive layer and an electron transport layer to form amedium of organic luminescent layers; and (2) modifying the thicknessdimension of at least one of the layers each of the layers includingmolecular components corresponding to the layer and having at least twosilicon moieties reactive to a hydroxy functionality and the layerscoupled one to another by Si—O bonds, the modification by reaction ofthe corresponding molecular components one to another to form Si—O bondsbetween the molecular components, and the modification in sequence ofthe provision of the layers.

[0042] In preferred embodiments of this inventive method, at least onesilicon moiety is unreacted after reaction with a hydroxy functionality.In highly preferred embodiments, modification then includes hydrolyzingthe unreacted silicon moiety of one of the molecular components to forma hydroxysilyl functionality and, condensing the hydroxysilylfunctionality with a silicon moiety of another molecular component toform a siloxane bond sequence between the molecular components.

[0043] In highly preferred embodiments, the silicon moieties arehalogenated or alkoxylated silane moieties. Such embodiments includemodifying the thickness dimension by hydrolyzing the unreacted silanemoiety of one of the molecular components to form a hydroxysilyl,functionality and condensing the hydroxysilyl functionality with asilane moiety of another molecular component to form a siloxane bondsequence between the molecular components.

[0044] While the organic luminescent conductive layers/medium of thisinvention can, be described as having a single organic hole injecting ortransporting layer and a single electron injecting or transportinglayer, modification of each of these layers with respect to dimensionalthickness or into multiple layers, as more specifically described below,can result in further refinement or enhancement of device performance byway of the light emitted therefrom. When multiple electron injecting andtransporting layers are present, the layer receiving holes is the layerin which hole-electron interaction occurs, thereby forming theluminescent or emissive layer of the device.

[0045] The articles/devices of this invention can emit light througheither the cathode or the anode. Where emission is through the cathode,the anode need not be light transmissive. Transparent anodes can beformed of selected metal oxides or a combination of metal oxides havinga suitably high work function. Preferred metal oxides have a workfunction of greater than 4 electron volts (eV). Suitable anode metaloxides can be chosen from among the high (>4 eV) work functionmaterials. A transparent anode can also be formed of a transparent metaloxide layer on a support or as a separate foil or sheet.

[0046] The devices/articles of this invention can employ a cathodeconstructed of any metal, including any high or low work function metal,heretofore taught to be useful for this purpose and as furtherelaborated in that portion of the incorporated patent referenced in thepreceding paragraph. As mentioned therein, fabrication, performance, andstability advantages can be realized by forming the cathode of acombination of a low-work function (<4 eV) metal and at least one othermetal. Available low work function metal choices for the cathode arelisted in cols. 19-20 of the aforementioned incorporated patent, byperiods of the Periodic Table of Elements and categorized into 0.5 eVwork function groups. All work functions provided therein are from Sze,Physics of Semiconductor Devices, Wiley, New York, 1969, p.366.

[0047] A second metal can be included in the cathode to increase storageand operational stability. The second metal can be chosen from among anymetal other than an alkali metal. The second metal can itself be a lowwork function metal and thus be chosen from the above-referenced listand having a work function of less than 4 eV. To the extent that thesecond metal exhibits a low work function it can, of course, supplementthe first metal in facilitating electron injection.

[0048] Alternatively, the second metal can be chosen from any of thevarious metals having a work, function greater, than 4 eV. These metalsinclude elements resistant to oxidation and, therefore, those morecommonly fabricated as metallic elements. To the extent the second metalremains invariant in the article or device, can contribute to thestability. Available higher work function (4 eV or greater) metalchoices for the cathode are listed in lines 50-69 of col. 20 and lines1-15 of col. 21 of the aforementioned incorporated patent, by periods ofthe Periodic Table of Elements and categorized into 0.5 eV work functiongroups. As described more fully in U.S. Pat. No. 5,156,918 which isincorporated herein by reference in its entirety the electrodes and/orsubstrates of this invention, have, preferably, a surface with polarreactive groups, such as a hydroxyl (—OH) group. Materials suitable foruse with or as electrodes and/or substrates for anchoring the conductivelayers and luminescent media of this invention should conform to thefollowing requirements: any solid material exposing a high energy(polar) surface to which layer-forming molecules can bind. These mayinclude: metals, metal oxides such as SiO₂, TiO₂, MgO, and Al₂O₃(sapphire), semiconductors, glasses, silica, quartz, salts, organic andinorganic polymers, organic and inorganic crystals and the like.

[0049] Inorganic oxides (in the form of crystals or thin films) areespecially preferred because oxides yield satisfactory hydrophilic metalhydroxyl groups on the surface upon proper treatment. These hydroxylgroups react readily with a variety of silyl coupling reagents tointroduce desired coupling functionalities that can in turn facilitatethe introduction of other organic components.

[0050] The physical and chemical nature of the anode materials dictatesspecific cleaning procedures to improve the utility of this invention.Alkaline processes (NaOH aq.) are generally used. This process willgenerate a fresh hydroxylated surface layer on the substrates while themetal oxide bond on the surface is cleaved to form vicinal hydroxylgroups. High surface hydroxyl densities on the anode surface can beobtained by sonicating the substrates in an aqueous base bath. Thehydroxyl groups on the surface will anchor and orient any of themolecular components/agents described herein. As described more fullybelow, molecules such as organosilanes with hydrophilic functionalgroups can orient to form the conductive layers.

[0051] Other considerations relating to the design, material choice andconstruction of electrodes and/or substrates useful with this inventionare as provided in the above referenced and incorporated U.S. Pat. No.5,409,783 and in particular cols. 21-23 thereof, such considerations aswould be modified by those skilled in the art in accordance with themolecular conductive layers, and assembly methods and objects of thepresent invention.

[0052] The conductive layers and/or organic luminescent medium of thedevices/articles of this invention preferably contain at least twoseparate layers, at least one layer for transporting electrons injectedfrom the cathode and at least one layer for transporting holes injectedfrom the anode. As is more specifically taught in U.S. Pat. No.4,720,432, incorporated herein by, reference in its entirety, the latteris in turn preferably at least two layers, one in contact with theanode, providing a hole injecting zone and a layer between the holeinjecting zone and the electron transport layer, providing a holetransporting zone. While several preferred embodiments of this inventionare described as employing at least three separate organic layers, itwill be appreciated that either the layer forming the hole injectingzone or the layer forming the hole transporting zone can be omitted andthe remaining layer will perform both functions. However, enhancedinitial and sustained performance levels of the articles or deevices ofthis invention can be realized when separate hole injecting and holetransporting layers are used in combination.

[0053] Porphyrinic and phthalocyanic compounds of the type described incols. 11-15 of the referenced/incorporated U.S. Pat. No. 5,409,783 canbe used to form the hole injecting zone. In particular, thephthalocyanine structure shown in column 11 is representative,particularly where X can be, but is not limited to, analkyltrichlorosilane, alkyltrialkoxysilane, dialkyldialkoxysilane, ordialkyldichlorosilane functionality and where the alkyl and alkoxygroups can contain 1-6 carbon atoms or is hydrogen. Preferredporphyrinic compounds are represented by the structure shown in col. 14and where R, T¹ and T² can be but are not limited to analkyltrichlorosilane, alkyltrialkoxysilane, dialkyldialkoxysilane, ordialkyldichlorosilane functionality and where the alkyl and alkoxygroups contain 1-6 carbon atoms or is hydrogen. (See, also, FIGS. 1A and1B, herein.) Preferred phthalocyanine- and porphyrin-based hole injection agents include silicon phthalocyanine dichloride and5,10,15,20-tetraphenyl-21H,23H-porphine silicon (IV) dichloride,respectively.

[0054] The hole transporting layer is preferably one which contains atleast one tertiary aromatic amine, examples of which are as described inFIGS. 2A-2C and Examples 1 and 2. Other exemplary arylamine corestructures are illustrated in U.S. Pat. No. 3,180,730, which isincorporated herein by reference in its entirety, where the corestructures are modified: as described herein. Other suitabletriarylamines substituted with a vinyl or vinylene radical and/orcontaining at least one active hydrogen containing group are disclosedin U.S. Pat. Nos. 5,409,783, 3,567,450 and 3,658,520. These patents areincorporated herein by reference in their entirety and the corestructures disclosed are modified as described herein. In particular,with respect to the arylamines represented by structural formulas XXIand XXII in cols. 15-16 of U.S. Pat. No. 5,409,703, R²⁴, R²⁵, R²⁶, R²⁷,R³⁰ and R³² can be an alkyltrichlorosilane, alkyltrialkoxysilane,dialkyldialkoxysilane, or dialkyldichlorosilane functionality where thealkyl and alkoxy groups can contain 1-6 carbon atoms or is hydrogen.

[0055] Molecular components of this invention comprising emissive agentsand/or the emissive layer include those described herein in FIGS. 3A-3Cand Example 5. Other such components/agents include various metalchelated oxinoid compounds, including chelates of oxine (also commonlyreferred to as 8-quinolinol or 8-hydroxyquinoline), such as thoserepresented by structure III in col. 8 of the referenced andincorporated U.S. Pat. No. 5,409,783, and where Z² can be but is notlimited to an alkyltrichlorosilane, alkyltrialkoxysilane,dialkyldialkoxysilane, or dialkyldichlorosilane functionality and wherethe alkyl and alkoxy groups can contain 1-6 carbon atoms or is hydrogen.Other such molecular components/emissive agents include theequinolinonlato compounds represented in cols. 7-8 of U.S. Pat. No.5,151,629, also incorporated herein by reference in its entirety, wherea ring substituent can be but is not limited to an alkyltrichlorosilane,alkyltrialkoxysilane, dialkyldialkoxysilane, or dialkyldichlorosilanefunctionality and where the alkyl and alkoxy groups can contain 1-6carbon atoms or is hydrogen. In a similar fashion, the dimethylidenecompounds of U.S. Pat. No. 5,130,603, also incorporated herein byreference in its entirety, can be used, as modified in accordance withthis invention such that the aryl substituents can include analkyltrichlorosilane, alkyltrialkoxysilane, dialkyldialkoxysilane, ordialkyldichlorosilane functionality and where the alkyl, and alkoxygroups can contain 1-6 carbon atoms or is hydrogen.

[0056] Other components which can be used as emissive agents includewithout limitation anthracene, naphthalene, phenanthrene, pyrene,chrysene, perylene and other fused ring compounds, or as provided incol. 17 of the previously referenced and incorporated U.S. Pat. No.5,409,783, such compounds as modified in accordance with this inventionand as more fully described above. Modifiable components also includethose described in U.S. Pat. Nos. 3,172,862, 3,173,050 and 3,710,167—allof which-are incorporated herein by reference in their entirety.

[0057] Molecular components which can be utilized as electron injectingor electron transport agents and/or in conjunction with an electroninjection or electron transport layer are as described in FIGS. 4A-4Cand Examples 3(a)-(d) and 4. Other such components include oxadiazolecompounds such as those shown in cols. 12-13 of U.S. Pat. No. 5,276,381,also incorporated herein by reference in its entirety, as such compoundswould be modified in accordance with this invention such that the phenylsubstituents thereof each include an alkyltrichlorosilane,alkyltrialkoxysilane, dialkyldialkoxysilane, or dialkyldichlorosilanefunctionality and where the alkyl and alkoxy groups can contain 1-6carbon atoms or is hydrogen. Likewise, such components can be derivedfrom the thiadiazole compounds described in U.S. Pat. No. 5,336,546which is incorporated herein by reference in its entirety.

[0058] As described above, silicon moieties can be used in conjunctionwith the various molecular components, agents, conductive layers and/orcapping layers. In particular, silane moieties can be used with goodeffect to impart mechanical, thermal, chemical and/or photochemicalstability to the luminescent medium and/or device. Such moieties areespecially useful in conjunction with the methodology described herein.Degradation is minimized until further synthetic modification isdesired. Hydrolysis an unreacted silicon/silane moiety provides an Si—OHfunctionality reactive with a silicon/silane moiety of anothercomponent, agent and/or conductive layer. Hydrolysis proceeds quickly inquantitative yield, as does a subsequent condensation reaction with anunreacted silicon/silane moiety of an other component to provide asiloxane bond sequence between components, agents and/or conductivelayers.

[0059] In general, the molecular agents/components in FIGS. 1-4 can beprepared with a lithium or Grignard reagent using synthetic techniquesknown to one skilled in the art and subsequent reaction with halosilaneor alkoxysilane reagents. Alternatively, unsaturated olefinic oracetylenic groups can be appended from the core structures using knownsynthetic techniques. Subsequently, halosilane or alkoxysilanefunctional groups can be introduced using hydrosilation techniques, alsoknown to one skilled in the art. Purification is carried out usingprocedures appropriate for the specific target molecule.

[0060] It has been observed previously that the performancecharacteristics of electroluminescent articles of the type describedherein can be enhanced by the, incorporation of a layer having adielectric function between the anode and, for instance, a holetransport layer. Previous studies show that the vapor, deposition ofthin layers of LiF onto anode before deposition of the other layer(s)improves performance in the areas of luminescence and quantumefficiency. However, this technique is limited in that the deposited LiFfilms are rough, degrade in air and do not form conformal, pinhole-freecoatings.

[0061] The present invention is also directed to the application ofself-assembly techniques to form layers which cap an electrode, providedielectric and other functions and/or enhance performance relative tothe prior art. Such capping layers, are self-assembled films which areconformal in their coverage, can have dimensions less than one nanometerand can be deposited with a great deal of control over the total layerthickness. Accordingly; the present invention also includes anelectroluminescent article or device which includes (1) an anode, (2) atleast one molecular capping layer coupled to the anode withsilicon-oxygen bonds, with each capping layer coupled one to anotherwith silicon-oxygen bonds, (3) a plurality of molecular conductivelayers, with one of the layers coupled to the capping layer withsilicon-oxygen bonds and each conductive layer coupled one to anotherwith silicon-oxygen bonds, and (4) a cathode in electric contact with aconductive layer. Likewise, and in accordance with this invention, thecapping layer can be deposited on a conductive layer and/or otherwiseintroduced so as to be adjacent to a cathode, to enhance overallperformance.

[0062] More generally and within the scope of this invention, the anodeis separated from the cathode by an organic luminescent medium. Theanode and cathode are connected to an external power source by,conductors. The power source can be a continuous direct, alternating orintermittent current voltage source. A convenient conventional, powersource including any desired switching circuitry, which is capable ofpositively biasing the anode with respect to the cathode, can beemployed. Either the anode or cathode can be at ground potential.

[0063] In preferred embodiments, each conductive and/or capping layerhas molecular components, and each molecular, component has at least twosilicon moieties. In highly preferred, embodiments, each such conductiveand/or capping component is a halogenated or alkoxylated silane, andsilicon-oxygen bonds are obtainable from the condensation of the silanemoieties with hydroxy functionalities. Without limitation, a preferredcapping material is octachlorotrisiloxane. The anode and cathode can bechosen and/or constructed as otherwise described herein.

[0064] In part, the present invention is a method of using moleculardimension to control the forward light output of an electroluminescentdevice. The inventive method includes (1) providing an electrode and amolecular layer thereon, the layer coupled to the electrode with firstmolecular components having at least two silicon moieties reactive to ahydroxy functionality, and (2) modifying the thickness of the layer byreacting the molecular components with second components to form asiloxane bond sequence between the first and second molecularcomponents, the second molecular components having at least two siliconmoieties, also reactive to a hydroxy functionality.

[0065] In preferred embodiments of this inventive method, at least onesilicon moiety is unreacted after reaction with a hydroxy functionality.In highly preferred embodiments, the modification further includeshydrolyzing an unreacted silicon moiety of one of the molecularcomponents to form a hydroxysilyl functionality and condensing thehydroxysilyl functionality with a silicon moiety of a third molecularcomponent to form a siloxane bond sequence between the second and thirdmolecular components. In highly preferred embodiments, the siliconmoieties are halogenated or alkoxylated silane moieties.

[0066] In part, the present invention also includes anyelectroluminescent article for generating light upon application of anelectrical potential across two electrodes. Such an article includes anelectrode having a surface portion and a molecular layer coupled and/orcapped thereon. The layer includes molecular components, and eachcomponent has at least two silicon moieties. The layer is coupled to theelectrode with silicon-oxygen bonds. In preferred embodiments, eachsilicon moiety is a halogenated silane, and silicon-oxygen bonds areobtained from a condensation reaction. Likewise, and without limitation,the electrode has a substrate with a hydroxylated surface portiontransparent to near IR and visible wavelengths of light. Such a layercan be utilized to cap the electrode and/or enhance performance asotherwise described herein. More generally, in such an article or anyother described herein, the luminescent medium can be constructed usingeither the self-assembly techniques described herein or the materialsand techniques of the prior art.

[0067] The present invention can be modified or otherwise used tocontrol charge migration and the resulting light emission. Micro contactprinting (SLCP) is a widely used soft-lithography technique tochemically pattern the surfaces of various substrates, on whichsubmicron or even nanometric features have been using selective physicalor chemical deposition techniques. Xia, Y.; Whitesides, G. M.; Angew.Chem. Int. Ed., 1998, 37, 550. The present invention provides a novelapproach to pixel fabrication of organic light-emitting diodes and/orrelated electroluminescent articles using micro-contact printing and/orsimilar chemical patterning methods. Such printing and/or patterningmethods are well-known to those skilled in the art and include, withoutlimitation, the following: micro-filtration membranes; Granstrom, M.;Berggren, M.; Inganas, O.; Science 1995, 27, 1479 inkjet printing;Hebner, T. R.; Wu, C. C.; Marcy, D.; Lu, M. H.; Sturm, J. C.; Appl.Phys. Lett. 1998, 72, 519. Bharathan, J.; Yang, Y., Appl. Phys. Lett.1998, 72, 2660. Chang, S.; Bharathan, J.; Yang, Y.; Helgespn, R.; Wudl,F.; Ramey, M. B.; Reynolds, J. R.; Appl. Phys. Lett. 1998, 73, 2561.solvent assisted micro-molding; Rogers, J. A.; Bao, Z.; Dhar, L.; Appl.Phys. Lett. 1998, 73, 294. and photoacid-activated chemicaltransformations. Renak, M. L.; Bazan, G. C.; Roitman, D.; Adv: Maater.1997, 9, 392 The present approach is compatible and can be used inconjunction with various such methods to make the present devices orarticles, such methods include thermal evaporation, spin coating, andmolecular self-assembly.

[0068] As discussed elsewhere, the articles, devices and/or diodes ofthis invention, including the luminescent media thereof and anymodifications thereto, can be prepared using various molecularcomponents/agents and/or conductive layers together with the fabricationand construction methods described herein. Accordingly, the presentinvention provides generally an electroluminescent article forgenerating light upon application of an electrical potential across twoelectrodes. Such an article can include (1) an anode; (2) a plurality ofmolecular conductive layers, one of the layers coupled to the anode withsilicon-oxygen bonds and the conductive layers coupled one to anotherwith silicon-oxygen bonds; (3) a cathode in electrical contact with theconductive layers; and (4) a molecular charge control layer coupled withsilicon-oxygen bonds to either one of the electrodes or the conductivelayers, with the control layer having a predetermined spatialdistribution of molecular components. In preferred embodiments, thecharge control layer is predetermined during design and fabrication toprovide a pattern of molecular components, such that the pattern definesat least one opening through the control layer to the electrode orconductive layer to which it is coupled. In highly-preferredembodiments, in accordance with this invention, a pattern of openingsprovides the article with a predetermined pixel array of emitted lightat wavelengths controlled as described elsewhere herein. Theconfigurations of such arrays are limited only by the techniques used toapply the patterns on the article during fabrication.

[0069] With reference to FIG. 12A, a charge control layer of thisinvention can be applied, bonded and/or coupled directly to an anode. Anapplication of such a patterned layer blocks or raises the energybarrier to hole injection into those regions of a hole transfer layer.With reference to FIGS. 12B and 12C, a patterned charge control layercan, alternatively, be coupled or applied to any one of the luminescentor conductive layers, such layers including but not limited to holetransport, electron transport and emissive layers. When patterned on ahole transport layer, a charge control layer blocks hole transport intothe electron transport layer and impedes emission of light by electronand hole recombination. When applied to or coupled with an electrontransport layer, a patterned charge control layer blocks or impedes inthose regions electron injection from the cathode into an electrontransport layer, also preventing emissive hole and electronrecombination. As with all such devices of this invention, enhancedemissive characteristics are observed through the pixel array. Inasmuchas many diode devices of the prior art exhibit inefficient electroninjection fabrication of such a device with a patterned control layer onan electron transport layer can be especially useful.

[0070] With reference to Example 12, a charge control layer of thepresent invention is preferably one providing an alklsiloxane pattern onthe electrode or conductive layer. Consistent with the methodologiesdescribed elsewhere herein, various silane molecular components can beused to provide the charge control layer and the resultingsilicon-oxygen bonds. In preferred embodiments, the silicon moiety ofsuch a molecular component is a halogenated silane, such that asilicon-oxygen bond is obtained from the condensation reaction of thesilane with a hydroxy functionality on either the electrode orconductive layer. Octadecyltrichlorosilane is one such preferredcomponent.

[0071] The controlled charge migration and light emission inherent tothe pixel array of this invention is a manifestation of the blocking orbarrier effect described above. On a molecular basis, this effect can beachieved by incorporation of the hydrophobic terminus opposite thereactive silicon moiety. While an octadecyl substituent is described aspart of a preferred molecular embodiment, a wide range of alkylsubstituents can be used with equal effect, such range as would bewell-known to those skilled in the art.

[0072] As inferred above, the present invention is also a method ofusing silicon molecular components of a luminescent medium to controlcharge migration within and the resulting light emission from anelectroluminescent device. As described above, such a medium can have aplurality of silicon molecular components, with a predetermined spatialdistribution of the components within the medium. This spatialdistribution controls hole/electron migration and emissiverecombination. For instance and without limitation, the siliconmolecular components of the conductive layer(s) of such a medium canhave two or more silicon moieties, while other silicon molecularcomponents have one silicon moiety. The patterned spatial distributionof such components can be used on a molecular level to direct chargemigration control the molecular dimension of the conductive portion of aluminescent medium and/or block or extinguish light transmission. Aswould be well known to those skilled in the art such a combination ofmolecular components and related factors can be used effectively toprovide a pixel array of the type described herein.

[0073] Generally, but with particular reference to the data andinformation provided in Example 15 and FIGS. 14-16, the presentinvention also provides a method of using molecular distribution tocontrol the turn-on voltages and light emission of an electroluminescentdevice. Use of one or more conductive layers, together with a controllayer provides a pattern and/or distribution of molecular components todirect or otherwise control charge migration, recombination andresulting light emission. Such a control layer can comprise molecularcomponents of the type described herein. In preferred embodiments, suchcomponents are printed on the applicable electrode or conductive layer.Micro-contact printing is a preferred method however, other physical orchemical deposition techniques can also be used. One of more conductivelayers can be incorporated into a device of this invention, preferablythrough the molecular self-assembly methods described herein. However,and without limitation, the same or analogous chemical, components canalso be utilized in conjunction with spin-coating techniques as morefully described in a co-pending application (Ser. No. 60/107,831)entitled “Organic Light-Emitting Diodes and Methods for Spin-CoatAssembly”, filed on Nov. 10, 1998 which is incorporated herein byreference in its entirety.

[0074] With particular reference to FIG. 16, an increase in voltageenhances the light emitted from the display. Initially, as voltage isapplied, light is directed through the pixel array. An increase involtage (dotted line reference in FIG. 16) results in lighting theentire luminescent display of such a device. Without restriction to anyone theory or mode of operation, it is believed that an increase involtage increases hole injection. At higher voltages, holes can tunnelthrough the printed control layer. Light is no longer directed throughthe pixel array, but emitted throughout the entire display. Accordingly,the molecular distribution and resulting pixel array can be used toprovide a voltage controlled 3-state display device: initial darkness, apatterned display at, low turn-on voltage, and a fully-lit, display athigher voltages.

[0075] With reference to FIG. 11 and Example 12, a stamp and/or mask canbe prepared having a relief structure corresponding to the pattern ofmolecular components to be applied on or contacted to an electrode orconductive layer. Structural variations can provide openings through thecontrol layer to the contacted surface. Such a pattern, together withsubsequent application of the appropriate conductive/luminescent layerprovides the predetermined spatial distribution of molecular componentsresulting in the desired pixel array.

EXAMPLES OF THE INVENTION

[0076] The following non-limiting examples and data illustrate variousaspects and features relating to the articles/devices and/or methods ofthe present invention, including the assembly of a luminescent mediumhaving various molecular components/agents and/or conducive layers, asare available through the synthetic methodology described herein. Incomparison with the prior art, the present methods and articles/devicesprovide results and data which are surprising, unexpected and contraryto the prior art. While the utility of this invention is illustrated inthe following examples and elsewhere through the use of severalarticles/devices and molecular components/agents/layers which can beused therewith, it will be understood by those skilled in the art thatcomparable results are obtainable with various other articles/devicesand components/agents/layers, as are commensurate with the scope of thisinvention.

Example 1

[0077]

[0078] Synthesis of a Silanated Hole Transport Agent [1]. With referenceto reaction scheme, above, hole transport components, agents and/orlayers can be prepared, in accordance with this invention and/or for usein conjunction with light-emitting diodes and other similarelectroluminescent devices. Accordingly, 500 mg. (1.0 mmole) oftrisbromophenylamine (Aldrich Chemical Company) was dissolved in 30 mlof dry dimethoxyethane (DME). This solution was cooled to −45° C. and1.2 ml (3.3 mmole) of a 2.5 M solution of n-butyl lithium in hexane wasadded to the reaction mixture. The entire mixture was then slowly warmedto 20° C. After stirring at 20° C. for an additional hour the solventwas removed in vacuo. The resulting white precipitate was washed (3×20ml) with dry pentane and redissolved in 30 ml dry DME. This solution wassubsequently poured into 10 ml (87 mmole) of silicon tetrachloride at arate of 1 ml/min. The entire reaction mixture was then refluxed for twohours. The resulting supernatent was separated from the precipitate andthe solvent again removed in vacuo yielding a green, brown residue. Awhite solid was obtained from this residue upon sublimation at 10⁻⁶torr. Characterization: ¹H NMR (600 MHz, C₆D₆, 20° C.): δ 7.07 (d, 6H,Ar—H); δ 7.05 (d, 6H, Ar—H); EI-MS (m/z): 645 (M+).

Example 2

[0079] With reference to FIGS. 2A-2C and the representative arylaminesprovided therein, other hole transport agents and/or layers of thisinvention can be obtained by straightforward application of thesilanation procedure described above in Example 1, with routinesynthetic modification(s) and optimization of reaction conditions aswould be well-known to those skilled in the art and as required by theparticular arylamine. Likewise, preliminary halogenation/bromination canbe effected using own synthetic procedures. Alternatively, thearylamines of FIGS. 2A-2C and other suitable substrates can be preparedusing other available synthetic procedures to provide multiple silanereaction centers' for use with the self-assembly methods andlight-emitting diodes of this invention. Core molecular substrates ofthe type from which the arylamines of FIGS. 2A-2C can be prepared aredescribed by Strukelii et al. in Science, 267, 1969 (1995), which isincorporated herein by reference in its entirety.

Example 3

[0080] Synthesis of a Silanated Electron Transport Agent. With referenceto Examples 3(a)-(d) and corresponding reaction schemes, below, electrontransport agents and/or layers can be prepared, in accordance with thisinvention and/or for use in conjunction with light-emitting diodes andother similar electroluminescent devices.

Example 3a

[0081] Synthesis of 4′-Bromo-2-(4-bromobenzoyl)acetophenone [2]. In a1-liter, three neck round bottom flask, 43 g (0.2 mol) methyl4-bromobenzoic acid and 17.6 g (0.4 mol) sodium hydride were dissolvedin 200 ml dried benzene and heated to 60° C. Next, 39.8 g (0.2 mol)4-bromoacetophenone in 100 ml dry benzene was slowly added through adropping funnel, and 1 ml methanol was added to the flask to initiatethe reaction. After the mixture was, refluxed overnight, the reactionwas quenched by adding methanol and pouring it into ice water. The pH ofthe mixture was brought down to 7.0 using 5 N sulfuric acid. A solid wascollected, washed with water, and recrystallized from benzene to give alight yellow product. Characterization. Yield: 30.3 g (40%). ¹H NMR (300MHz, CDCl₃, 2020 C., δ): 7.84 (d, 4H, ArH); 7.62 (d, 4H, ArH); 6.77 (s,2H, CH₂). EI-MS: 382(M+), 301, 225, 183, 157.

Example 3b

[0082] Synthesis of 3,5-Bis(4-bromophenyl)isoxazole [3]. In a 250 mlround bottom flask, 4 g (10.4 mmol) of [2] was dissolved in 100 ml drydioxane and heated to reflux, then 3.0 g (43.2 mmol) hydroxylaminehydrogen chloride in 10 ml water and 5 ml (25 mmol) 5 N NaOH was thendropped into the refluxing mixture. After 12 hours, the reaction mixturewas cooled down to room temperature, and the solvent was removed invacuo. The product was recrystallized from ethanol. Characterization.Yield: 3.41 g (85%). M.P. 218.5-219.5° C. ¹HNMR (300 MHz, CDCl₃, 20° C.,δ): 7.78(d, 2H, ArH), 7.74 (d, 2H, Ar′H), 7.66 (d, 2H, Ar′H), 7.62 (d,2H, ArH), 6.82 (s, 114, isoxazole proton). EI-MS: 379(M+), 224, 183,155.

Example 3c

[0083] Synthesis of 3,5-Bis(4-allylphenyl)isoxazole [4]. In a 250 mlthree-neck round bottom flask, 3.77 g (10 mmol) of [3], 460 mg. (0.4mmol) tetrakis(triphenylphosphine) palladium, and 7.28 g (22 mmol)tributylallyltin were dissolved in 100 ml. dried toluene and degassedwith nitrogen for 30 min. The mixture was heated to 100° C. for 10 h,then cooled down to room temperature. Next, 50 ml. of a saturatedaqueous ammonium fluoride solution was subsequently added to themixture. The mixture was extracted with ether, and the combined organiclayer was washed by water, then brine, and finally dried over sodiumsulfate. The solvent was removed in vacuo. The residue was purified bycolumn chromatography. (first, 100% hexanes, then chloroform:hexanes[80:20]). Characterization. Yield: 1.55 g (57%). ¹H NMR (300 MHz, CDCl₃,20° C., δ): 7.78(d, 2H, ArH), 7.74 (d, 2H, Ar′H), (d, 2H, ArH), 7.30(d,2H, Ar′H), 6.78 (s, 1H, isoxazole proton), 5.96 (m, 2H, alkene H), 5.14(d, 4H, terminal alkene H), 3.44 (d, 4H, methylene group). EI-MS:299(M+), 258, 217.

Example 3d

[0084] Synthesis of 3,5-Bis(4N-trichlorosilyl)propylphenyl)isoxazole[5]. To 2 ml of THF was added 5 mg of [4], 3.4 μl of HSiCl₃ and 0.8 mgof H₂PtCl₆ were added to 2 ml of THF. The reaction was heated at 50° C.for 14 h. The solvent was then removed in vacuo. A white solid wasobtained from this residue upon sublimation at 10⁻⁶ torr.Characterization ¹H NMR (300 MHZ, d⁸-THF, 20° C., δ): 7.72(d, 2H, Ar′H),7.68 (d, 2H, Ar′H), 7.36 (d, 2H, ArH), 7.32 (d, 2H, Ar′H), 6.30(s, 1H,isoxazole); 2.52(t, 2H, CH); 1.55(m, 4H, CH₂); 0.85 (t, 6H, CH₃).

Example 4

[0085] With reference to FIGS. 4A-4C and the representative heterocyclesprovided therein, other electron transport agents and/or layers of thisinvention can be obtained by straight-forward application of thesilanation procedure described above in Example 3, with routinesynthetic modification(s) and optimization of reaction conditions aswould be well-known to those skilled in the art and as required by theparticular heterocyclic substrate. Preliminary halogenation/brominationcan be effected using known synthetic procedures or through choice ofstarting materials enroute to a given heterocycle. Alternatively, theheterocycles of FIGS. 4A-4C and other suitable substrates can beprepared using other available synthetic procedures to provide multiplesilane reaction centers for use with the self-assembly methods andlight-emitting diodes of this invention. Core molecular substrates ofthe type from which the heterocycles of FIGS. 4A-4C can be prepared arealso described by Strukelji et al. in Science, 267, 1969 (1995).

Example 5

[0086] With reference to FIGS. 3A-3C and the representative chromophoresprovided therein, missive agents and/or layers, in accordance with thisinvention, can be obtained by appropriate choice of starting materialsand using halogenation and silanation procedures of the type describedin Examples 1-4, above. Alternatively, other chromophores can besilanated using other available synthetic procedures to provide multiplesilane reaction centers for use with the self-assembly methods andlight-emitting diodes of this invention. Regardless, in accordance withthis invention, such emissive agents or chromophores can be used foremission of light at wavelengths heretofore unpractical or unavailable.Likewise, the present invention allows for the use of multiple agents orchromophores and construction of an emissive layer or layers such that acombination of wavelengths and/or white light can be emitted.

Example 6

[0087] Examples 6(a)-6(c) together with FIG. 6 illustrate thepreparation of other molecular components which can be used inaccordance with this invention.

Example 6a

[0088] Synthesis of Tertiary Arylamine [6]. Together, 14.46 g (20 mmole)of tris(4-bromophenyl)amine and 500 ml of dry diethyl ether were stirredat −78° C. under a nitrogen atmosphere. Next, 112.5 ml of a 1.6 Mn-butyllithium solution in hexanes was slowly added to, the reactionmixture over 1.5 hours. The reaction was then warmed to −10° C. andstirred for an additional 30 minutes. The reaction was then cooled downagain to −78° C. before the addition of 22 g (0.5 mole) of ethyleneoxide. The mixture was stirred and slowly warmed to room temperatureover 12, hours. Next, 2 ml of a dilute NH₄Cl solution was then added tothe reaction mixture. The solvent was evaporated under vacuum yielding alight green solid. The product was purified using column chromatography.The column was first eluted with chloroform and then with MeOH:CH₂Cl₂(5:95 v/v). The resulting light gray solid was recrystallized usingchloroform to give 1.89 g. Yield: 25%. ¹H NMR (δ, 20° C., DMSO): 2.65(t,6H), 3.57 (q,6H), 4.64 (t,3H), 6.45 (d,6H), 7.09 (d,6H). EI-MS: 377(M⁺), 346 (M+−31), 315 M+−62). HRMS: 377.2002. calcd; 377.1991. Anal.Calculated for C₂₄H₂₇NO₃; C, 76.36; H, 7.21; N, 3.71. Found: C, 76.55;H, 7.01; N, 3.52.

Example 6b

[0089] Synthesis of Tosylated Arylamine [7]. A pyridine solution oftosyl chloride (380 mg in 5 ml) was added over 5 minutes to a pyridinesolution of [6] (500 mg in 10 ml, from Example 6a) cooled to 0° C. Themixture was stirred for 12 hours, then quenched with water and extractedwith chloroform. The organic extract was washed with water, 5% sodiumbicarbonate, and dried with magnesium sulfate. After filtration, thechloroform solution was then evaporated to dryness under vacuum andpurified using column chromatography. The column was first eluted withhexane:CHCl₃ (1:2 v/v) yielding [7]. ¹H NMR (300 MHz, δ, 20° C., CDCl₃):2.45 (s,3H), 2.90 (t,6H), 3.02 (t,3H,3.70 (t,3H), 4.19 (t,6H), 6.92(d,2H), 6.98 (d,4H), 7.00 (d,4H), 711 (d,2H), 7.32 (d,2H), 7.77 (d,2H).

Example 6c

[0090] Synthesis of Tosylated Arylamine [8]. Continuing thechromatographic procedure similar for 2 (from Example 6b) but changingthe eluting solvent to 100% CHCl₃ yielded [8]. ¹H NMR (300 MHz, δ, 20°C., CDCl₃): 2.44 (s,6H), 2.91 (t,3H), 3.02 (t,6H), 3.70 (t,6H), 4.19(t,3H), 6.92 (d,4H), 6.98 (d 7.00 (d,2H), 7.11 (d,4H), 7.32 (d,4H), 7.77(d,4H).

Example 7

[0091] Using the arylamines of Examples 6 and with reference to FIG. 7,an electroluminescent article/device also in accordance with thisinvention is prepared as described, below. It is understood that thearylamine component can undergo another or a series of reactions with asilicon/silane moiety of another molecular component/agent to provide asiloxane bond sequence between components, agents and/or conductivelayers. Similar electroluminescent articles/devices and conductivelayers/media can be prepared utilizing the various other molecularcomponents/agents and/dr layers described above, such as in Examples 1-5and FIGS. 1-4, in conjunction with the synthetic modifications of thisinvention and as required to provide the components with the appropriatereactivity land functionality necessary for the assembly method(s)described herein.

Example 7a

[0092] This example of the invention shows how slides can beprepared/cleaned prior to use as or with electrode materials. Anindium-tin-oxide (ITO)-coated soda lime glass (Delta Technologies) wasboiled in a 20% aqueous solution of ethanolamine for 5 minutes, rinsedwith copious amounts of distilled water and dried for 1 hour at 120° C.;alternatively and with equal effect, an ITO-coated soda lime glass(Delta Technologies) was sonicated in 0.5M KOH for 20 minutes, rinsedwith copious amounts of distilled water and then ethanol, and dried for1 hour at 120° C.

Example 7b,

[0093] Electroluminescent Article Fabrication and Use. The freshlycleaned ITO-coated slides were placed in a 1% aqueous solution of3-aminopropyltrimethoxysilane and then agitated for 5 minutes. Thesecoated slides were then rinsed with distilled water and cured for 1 hourat 120° C. The slides were subsequently placed in a 1% toluene solutionof [7] (or [8] from Example 6) and stirred for 18 hours under ambientconditions. Afterwards, the slides were washed with toluene and curedfor 15 minutes at, 120° C. AlQ₃ (or GaQ₃; Q=quinoxalate) was vapordeposited on top of the amine-coated slides. Finally, 750-1000 Å ofaluminum was vapor deposited over the metal quinolate layer. Wires wereattached to the Al and ITO layers using silver conducting epoxy(CircuitWorks™), and when a potential (<7V) was applied, red, orange,and/or green light was emitted from the device. Example

Example 8

[0094] One or more capping layers comprising Cl₃SiOSiCl₂OSiC₃ aresuccessively deposited onto clean ITO-coated glas's where hydrolysis ofthe deposited material followed by thermal curing/crosslinking in air at125° C. yields a thin (˜7.8 Å) layer of material on the ITO surface.X-ray reflectivity measurements indicate that the total film thicknessincreases linearly with repeated layer deposition as seen in FIG. 8.Other molecular components can be used with similar effect. Suchcomponents include, without limitation, the bifunctional siliconcompounds described in U.S. Pat. No. 5,156,918, at column 7 andelsewhere therein, incorporated by reference herein in its entirety.Other useful components, in accordance with, this invention includethose trifuctional compounds which-cross-link upon curing. As would bewell known to those skilled in the art and made aware of this invention,such components include those compounds chemically reactive with boththe electrode capped and an adjacent conductive layer.

Example 9

[0095] Cyclic voltametry measurements shown in FIG. 9 using aqueousferri/ferrocyanide show that there is considerable blocking of theelectrode after the deposition of just one layer of the self-assembledcapping material specified in Example 8. Other molecular componentsdescribed, above, show similar utility, Almost complete blocking, asmanifested by the absence of pinholes, is observed after application ofthree layers of capping material.

Example 10

[0096] Conventional organic electroluminescent devices consisting of TPD(600 Å)/ Alq (600 Å)/Mg (2000 Å) were vapor-deposited on ITO substratesmodified with the capping material specified in Example 8. FIGS. 10A-Cshow the behavior of these devices with varying thickness of theself-assembled capping material. These results show that such a materialcan be used to modify forward light output and devicequantum-efficiency. For a device with two capping layers, higher currentdensities and increased forward light output are achieved at lowervoltages, suggesting an optimum thickness of capping material can beused to maximize performance of an electroluminescent article.

Example 11

[0097] This example illustrates how a capping material can be introducedto and/or used in the construction of an electroluminescent article.ITO-coated glass substrates were cleaned by sonication in acetone for 1,hour followed by sonication in methanol for 1 hour. The dried substrateswere then reactively ion etched in an oxygen plasma for 30 seconds.Cleaned substrates were placed in a reaction vessel and purged withnitrogen. A suitable silane, for instance a 24 mM solution ofoctachlorotrisiloxane in heptane, was added to the reaction vessel in aquantity sufficient to totally immerse the substrates. (Other suchcompounds include those described in Example 8). Substrates were allowedto soak in the solution under nitrogen for 30 minutes. Following removalof the siloxane solution the substrates were washed and sonicated infreshly distilled pentane followed by a second pentane wash undernitrogen. Substrates were then removed from the reaction vessel washedand sonicated in acetone. Substrates were dried in air at 125° C. for 15minutes. This process can be repeated to form a capping layer ofprecisely controlled thickness. Capping layer(s) can likewise be used inconjunctions with other embodiments of the present invention, wherethose embodiments would benefit by the functional advantages provided bysuch a modification.

Example 12

[0098] A patterned silicon mask was made using conventionalphotolithographic techniques. The test pattern consisted of a series ofcylinders with cross-sectional diameters of 10 μM-50 μM extending fromthe surface of the mask. The distance between two cylinders was 100 μM.Based on this mask, polydimethylsiloxane (PDMS) stamps were preparedaccording to the reported procedure. ITO coated glass plates wereprovided by Donnelly Comp any with a sheet resistance of 20 Ω/sq. Thecutting, patterning, and cleaning procedures are well-known to thoseskilled in the art. See, for instance, Jabbour G. E., Kawabe, Y.;Shaheen, S. E.; Wang, J. F.; Morrell, M. M.; Kyppelen, B.; Peyghabarian,N.; Appl. Phys. Lett. 1997, 17, 1762. Next, a suitable hydrolyzablesilane or silicon moiety, such as 10 μM octadecyltrichlorosilane (OTS)solution in toluene, was used to ink the PDMS stamps, and to printpatterns on ITO substrates for, control of charge migration lightemission. The basic inking and printing procedures are also well-known.See, for instance, Kumar, A.; Biebuyck, H. A.; Whitesides, G. M.;Langmuir 1994. 10, 1948. FIG. 11 schematically shows the procedure ofthis example.

Example 13

[0099] This example illustrates fabrication of a device having an arrayof pixels, in accordance with this invention. A conventional smallmolecule deposition method was used to, fabricate an electroluminescentdevice on a substrate patterned as described herein. The base pressurewas 5×10⁻⁶ torr.N-N′-diphenyl-N-N′bis(3-methylphenyl)-[1-1′-biphenyl]-4-4′-diamine (TPD)was employed as a hole transport layer (HTL) and used as received, while8-tris-hydroxyquinoline aluminum (Alq₃) was purified using vacuumsublimation and used as the emissive and electron transport layer(ENM/ETL). Aluminum was used as the cathode and was thermally depositedin another chamber having a base pressure of 5×10⁻⁶ torr. The resultingdevice structure and layer thicknesses are shown in schematically inFIG. 12.

Example 14

[0100] The electroluminescent devices of this invention can becharacterized in an enclosed anaerobic aluminum sample holder under anN₂′ environment. A Keithley 2400 source meter supplied d.c. voltage tothe devices and simultaneously recorded the current flowing through thedevices. At the same time, an IL 1700 research radiometer with acalibrated silicon photodetector was used to collect the deviceemission. These instruments were controlled by a PC using Lab Viewsoftware. Light-emitting pixel arrays were imaged with an opticalmicroscope under ambient conditions. The photographs of FIG. 13 weretaken without external illumination.

Example 15

[0101]FIGS. 14 and 15 show the current—voltage and light output—voltagecurves for a patterned device, in accordance with the methods, articlesand/or molecular structures of this invention. The insets expand the 15V-18 V region. From these curves, it can be seen that pixels, as can beprovided by the present control layer(s), can begin to turn on at ˜12 V.Although the total light output for the tested device is less thanoptimal at this voltage, the pixel arrays can be clearly observed underan optical microscope. The turn-on voltage is lower than that of anonpatterned bare ITO device, which is fabricated under the sameconditions. The nonpatterned device turns on at 15 V. This phenomenon isattributed to a strongly enhanced electric field at the pixel edges. Asthe applied voltage is increased, the pixels become brighter andbrighter with negligible light emission from the control layer-coveredareas until ˜16.75 V. The rapid increase of brightness with increasingapplied voltage above 16.75 V (insets of FIG. 3), indicates turning onof the covered areas. At 16.75 V. the measured light output from thepatterned device is 20 cd/m². Considering the effective device area is˜5% of the total area, the light output from an unpatterned deviceshould be ˜400 cd/m², which is higher than that required for displaypurposes (100-200 cd/m²). The pixel arrays were observed under anoptical microscope. Bright green spots can be clearly seen using adevice fabricated in this manner. Other wavelengths or combinations ofwavelengths are available and can be provided as described elsewhereherein. As referenced above, FIG. 13 shows a photograph of the resultingpixel array.

[0102] While the principles of this invention have been described inconnection with specific embodiments, it should be understood clearlythat these descriptions are added only by way of example and are notintended to limit, in any way the scope of this invention. For instance,the present invention can be applied more specifically to theconstruction of second-order nonlinear optical materials as have beendescribed in U.S. Pat. No. 5,156,918 which is incorporated herein byreference in its entirety. Another advantages and features will becomeapparent from the claims hereinafter, with the scope of the claimsdetermined by the reasonable equivalents, as understood by those skilledin the art.

What is claimed is:
 1. An electroluminescent article for generatinglight upon application of an electrical potential across two electrodes,said article comprising: an anode; a plurality of molecular conductivelayers, one of said layers coupled to said anode with silicon-oxygenbonds and said conductive layers coupled one to another withsilicon-oxygen bonds; a cathode in electrical contact with said,conductive layers; and a molecular charge control layer coupled withsilicon-oxygen bonds to one of said electrodes or said conductivelayers, said control layer having a predetermined spatial distributionof molecular components.
 2. The article of claim 1 wherein said chargecontrol layer has a pattern of molecular components, said patterndefining at least one opening through said charge control layer.
 3. Thearticle of claim 2 having a pixel array.
 4. The article of claim 2wherein said patterned charge control layer is coupled to said anode. 5.The article of claim 4 wherein said patterned charge control layer iscoupled to one of said conductive layers, said layers selected from thegroup consisting of hole transport, electron transport and emissivelayers.
 6. The article of claim 1 wherein each of said control layermolecular components has a silicon moiety.
 7. The article of claim 6wherein said silicon moiety is a halogenated silane, and each saidsilicon-oxygen bond is obtained from the condensation reaction of saidsilane with a hydroxy functionality.
 8. The article of claim 6 whereineach of said control layer molecular components has a hydrophobicterminus.
 9. The article of claim 1 wherein said anode comprises asubstrate having a hydroxylated surface portion.
 10. An organicelectroluminescent article for controlled light emission uponapplication of an electrical potential across two electrodes, saidarticle comprising a conductive layer, an electrode having a surfaceportion in electrical contact with said conductive layer, and apatterned molecular layer having a spatial distribution of molecularcomponents coupled to one of said electrodes or said conductive layer.11. The article of claim 10 wherein said patterned layer defines atleast one opening to said electrode.
 12. The article of claim 11 havinga pixel array.
 13. The article of claim 10 wherein each of saidpatterned layer molecular components has a silicon moiety.
 14. Thearticle of claim 13 wherein said silicon moiety is a halogenated silane,and each said silicon-oxygen bond is obtained from the condensationreaction of said silane with a hydroxy functionality.
 15. The article ofclaim 13 wherein each of said patterned layer molecular components has ahydrophobic terminus.
 16. The article of claim 10 wherein saidconductive layer is coupled to said electrode with silicon-oxygen bonds,said conductive layer comprising molecular components and each saidcomponent having at least two silicon moieties.
 17. The article of claim16 wherein said conductive layer comprises a plurality of sublayers ofmolecular components, each said molecular component having at least twosilicon moieties, and said sublayers coupled one to another withsilicon-oxygen bonds.
 18. A method of using the silicon molecularcomponents of a luminescent medium to control charge migration and lightemission within an electroluminescent device, said method comprising:coupling an organic luminescent medium adjacent to an anode, said mediumhaving a plurality of silicon molecular components and a predeterminedspatial distribution of said components therein, said medium coupled tosaid anode with silicon-oxygen bonds; providing said medium adjacentsaid anode at least one of a hole injection zone and a hole transportzone; and migrating positive charge carriers through said medium foremissive interaction with negative charge carriers generated by saiddevice.
 19. The method of claim 18 wherein said hole transport zoneincludes a plurality of molecular components, each said component havingat least two silicon moieties reactive with said anode to formsilicon-oxygen bonds between said anode and said hole transport zone.20. The method of claim 18 wherein said luminescent medium is modifiedby a pattern of silane molecular components on said anode.
 21. Themethod of claim 20 wherein said pattern defines exposed surface areas ofsaid anode.
 22. The method of claim 21 wherein said pattern provides apixel array.
 23. A method of using molecular distribution to control theturn-on voltages and light emission of an electroluminescent device,said method comprising: providing a first electrode; coupling aconductive layer to said electrode, said conductive layer comprisingmolecular components distributed on said electrode; providing a secondelectrode in electrical contact with said conductive layer; andcontacting a control layer on one of said electrodes or said conductivelayer in a predetermined pattern of molecular components, said patterndefining at least one opening through said control layer.
 24. The methodof claim 23 wherein said patterned control layer is printed with a stamphaving a relief structure in a contacting surface of said stamp.
 25. Themethod of claim 24 wherein said pattern of molecular components has aplurality of defining a pixel array.
 26. The method of claim 25 whereinsaid conductive molecular components are distributed in said openings ofsaid control layer for charge migration through said pixel array. 27.The method of claim 23 wherein each of said control layer molecularcomponents has a reactive silicon moiety and a hydrophobic terminus. 28.The method of claim 27 wherein said control layer contact providessilicon-oxygen bonds.
 29. The method of claim 28 wherein said controllayer contacts said conductive layer, said layer selected from the groupconsisting of hole transport, election transport and emissive layers.30. The method of claim 23 further including adjustment of voltage toincrease light emission through said control layer opening.
 31. Themethod of claim 30 wherein higher voltage increases hole injection. 32.The method of claim 31 wherein increasing voltage injects holes throughsaid control layer to provide light emission throughout said conductivelayer.